null safety

lib/pages/market/market_editor.dart

@@ -35,7 +35,7 @@ class _MarketEditorState extends State<MarketEditor> {
         children: <Widget>[
           Expanded(
             child: new Text(
-              p.name,
+              p.name ?? "",
               style: TextStyle(
                 fontSize: 15.0,
               ),
@@ -117,7 +117,7 @@ class _MarketEditorState extends State<MarketEditor> {
     });
     MarketModel marketModel = Provider.of<MarketModel>(context, listen: false);
     try {
-      await marketModel.deleteMarket(market.id);
+      await marketModel.deleteMarket(market.id!);
     } catch (e) {
       showMsgDialog(context, "Error", e.toString());
     } finally {

lib/pages/market/model/market_model.dart

@@ -20,14 +20,14 @@ class MarketModel extends BaseModel {
     try {
       if (listener != null) listener.cancel();
 
-      listener = Firestore.instance
+      listener = FirebaseFirestore.instance
           .collection("/$config_collection/$setting_doc_id/$markets_collection")
           .snapshots()
           .listen((QuerySnapshot snapshot) {
         markets.clear();
-        markets = snapshot.documents.map((documentSnapshot) {
+        markets = snapshot.docs.map((documentSnapshot) {
           var user = Market.fromMap(
-              documentSnapshot.data, documentSnapshot.documentID);
+              documentSnapshot.data as Map<String, dynamic>, documentSnapshot.id);
           return user;
         }).toList();
         notifyListeners();